Causation, Torts, and Epidemiologic Evidence

Tort law writers naturally focus on the changes in tort doctrine, such as the advent of strict liability and the demise of privity of contract, as catalysts for the development of mass tort law. There were, however, causes external to the world of tort law itself. One significant cause was the development of epidemiologic evidence and the acceptance of stochastic concepts of causation. Epidemiology is built upon statistical and probabilistic thinking, and the law struggled to accept such thinking in place of the comfortable mechanistic approaches to causation that dominated the law in the 19th and early 20th centuries. Although one can find examples of epidemiologic studies in the medical literature before 1940, the discipline of epidemiology was poorly developed, both in terms of its statistical tools, and in terms of its acceptance as a legitimate scientific approach, until after World War II. The U.S. Surgeon General’s acceptance of tobacco smoking as a cause of lung cancer, in the mid-1960’s, without any clear mechanistic model of causation, was a major turning point for both epidemiologic science and the law. Interestingly, this turning point occurred at the same time that the American Law Institute accepted the “strict liability” concept of tort liability for harms caused by defects in consumer products.

The epidemiologic study is a relative newcomer to the law of evidence, and many courts, commentators, and lawyers still talk of the admissibility (vel non) of such a study. Such talk is imprecise and inaccurate; rarely will a study itself be admissible. A typical observational epidemiologic study (or for that matter, a randomized clinical trial) involves many levels of hearsay, including statements of study participants, statements of the study investigators to the participants to elicit their self-reported symptoms and diagnoses, statements and conclusions of the investigators who assessed and characterized exposure and health outcomes, statements and conclusions of investigators who collected, analyzed, and reported the study data, the statements of the peer reviewers and editors who called for changes in how the study would be reported, and so on, and so forth.

Perhaps the initial layer of hearsay from study participants could be considered admissible under Rule 803(4), which creates an exception for:

“Statements for purposes of medical diagnosis or treatment.—
Statements made for purposes of medical diagnosis or
treatment and describing medical history, or past or present
symptoms, pain, or sensations, or the inception or general
character of the cause or external source thereof insofar as
reasonably pertinent to diagnosis or treatment.”

Statements made by study participants to study investigators, however, are typically made for neither diagnosis or treatment. In a case-control study, for instance, the cases are already diagnosed, and the purpose of the study is not treatment. The control participants are selected because they have no diagnosis, and they certainly are not in need of any treatment. Rule 803(4) seems not to fit.

Perhaps the Rule 803(6) would permit the records in the form of questionnaires, laboratory reports, exposure assessments, to be admitted as business records:

“Records of regularly conducted activity.—A memorandum,
report, record, or data compilation, in any form, of acts,
events, conditions, opinions, or diagnoses, made at or near the
time by, or from information transmitted by, a person with
knowledge, if kept in the course of a regularly conducted business
activity, and if it was the regular practice of that business
activity to make the memorandum, report, record or data
compilation, all as shown by the testimony of the custodian or
other qualified witness, or by certification that complies with
Rule 902(11), Rule 902(12), or a statute permitting certification,
unless the source of information or the method or circumstances
of preparation indicate lack of trustworthiness. The
term ‘business’ as used in this paragraph includes business,
institution, association, profession, occupation, and calling of
every kind, whether or not conducted for profit.”

Even if one or another layer of hearsay could be removed, it is difficult to imagine that all the layers could fit into exceptions that would allow the study itself to be admitted. Furthermore, even if the study were admitted, the language and statistical analyses would not be appropriately used as direct evidence without the explanatory input of an expert witness. Epidemiologic evidence is thus virtually always not admissible evidence at all, but rather part of the “facts and data” upon which expert witnesses have relied to formulate their opinions. Epidemiologic studies are those otherwise inadmissible materials considered by expert witnesses, and because they are themselves largely inadmissible, Rules 703 and 705 govern whether, how, and when such studies will be disclosed to the trier of fact.

It is interesting to consider the admissibility of another research, investigatory tool, the survey, to help us understand the law’s consideration of epidemiologic studies. One frequently cited case provides a useful history and summary of what would be required to admit a survey and its results, when offered for the truth:

“The trustworthiness of surveys depends upon foundation evidence that
(1) the “universe” was properly defined,
(2) a representative sample of that universe was selected,
(3) the questions to be asked of interviewees were framed in a clear, precise and non-leading manner,
(4) sound interview procedures were followed by competent interviewers who had no knowledge of the litigation or the purpose for which the survey was conducted,
(5) the data gathered was accurately reported,
(6) the data was analyzed in accordance with accepted statistical principles and
(7) objectivity of the entire process was assured.”

Toys “R” Us, Inc. v. Canarsie Kiddie Shop, Inc., 559 F. Supp. 1189, 1205 (E.D.N.Y. 1983). The court noted that admitting survey evidence should normally include the testimony of the survey director, supervisor, interviewers, and interviewees. The absence of one or more of the seven identified indicia of survey trustworthiness may require the exclusion of the survey. Id. (excluding the survey at issue for failing to satisfy the indicia of trustworthiness).

A further important lesson of Toys “R” Us is that an expert witness cannot save an otherwise untrustworthy survey under the cloak of Rule 703. The court, having excluded the survey as direct evidence, went on to exclude the expert witness opinion testimony based upon the survey. Id. (relying upon Rule 703 and case law and treatises interpreting this rule).

This case has an important lesson to lawyers litigating mass tort cases that turn on epidemiologic evidence of harm. If the study is untrustworthy in the light of the seven Toys “R” Us criteria, then the study may not be sufficiently reliable for an expert witness to rely upon under Rule 703. A further lesson is that many of the criteria can be answered only by accessing the underlying data and materials from the study. Many lawyers seem to have lost track of the importance of Rule 703, after the Supreme Court placed its reliance upon Rule 702 to support a requirement of expert witness gatekeeping. Rule 702, however, addresses “sufficiency” of facts and data, and the reliability of methods and principles, not the reasonableness of reliance upon the underlying facts and data themselves.

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